Keeping it somewhat vague for the sake of boredom the way a splitter works is it provides a surface area for high pressure air to push down on and that's how it creates downforce. A splitter's design is simple, but how it's mounted is what truly makes it functional. Think of it like a shelf. You make a shelf out of cardboard and duct tape it to a wall, then you put a 1 lb. weight on it and what happens? The shelf flexes and the weight falls off. So next you make the shelf out of super strong steel, there's no way it will flex or bend, but you still duct tape it to the wall. Now you can add 3 lbs. before the entire thing rips off the wall. Now you finally mount your steel shelf to the wall using big brackets and you mount them straight to the studs. Now all of a sudden you can load up 400 lbs. on that shelf without it flexing or ripping off the wall.
The wall is the car, the studs are the car's chassis, the weight is downforce, and the shelf is the splitter. A splitter mounted to the bumper cover using double stick tape and a few self tapping screws is going to do nothing. Likely the first step will be that the front edge of the lip flexes downward and the air starts bleeding off back underneath the car lowering the high pressure area that causes downforce. The little downforce that it will still make is only being used to flex and bend the bumper cover. Then lets say it still somehow continues to make more downforce, how much can it make before the double stick tape and self tapping screws give way?
A true splitter is mounted directly to the chassis, completely independent of the bumper cover and made of rigid material that does not flex that way it maintains a high amount of downward pressure 100% of which is pulling down directly on the chassis.
If you can't stand on it, its not working.
